Paste of paramagnetic particles for use in the examination of paramagnetic materials for flaws by the magnetic method



Patented Feb. 1, 1938 UNITED STATES PATENT OFFICE PASTE 0F PARAMAGNETIC PARTICLES EOE USE IN THE EXAMINATION 0F PARAMAG- NETIC MATERIALS FOR FLAWS BY THE MAGNETIC METHOD of Pennsylvania No Drawing. Application December 12, 1936, Serial No. 115,840-

scmm. (01.1'15-183) This invention relates to a paste of paramagneticparticles for use in the examination of paramagnetic materials for flaws by the magnetic method.

In the magnetic method of examining articles made of iron or steel or other paramagnetic material for the detection of cracks and flaws it has been customary in the past to use a fine iron powder, finely ground mill-scale or. the like, by dusting the dry powder over the surfaces of the previously magnetized articles undergoing examination. The use of such powders suspended in a liquid bath of a light oil or water has also been suggested and attempted but with rather indifferent success, especially where very fine cracks or flaws are to be detected. The lack of success, using such powders, has been due to the fact that the powders were of such high specific gravity and of such coarse particle size that the particles would not stay suspended in the liquid medium, and also to the fact that the particle size was too coarse to show very fine cracks, which produce only a relatively weak external leakage field that is capable of holding only very flne particles of very small mass.

The present invention overcomes these difiiculties by utilizing a powder of paramagnetic material of very fine size, in general less than 5 microns, and by employing a dispersing agent capable of preventing agglomeration of the particles and of effecting uniform dispersion thereof upon dilution of the paste to form a testing bath. The fine particles of paramagnetic material in the testing bath are thus free to move and align themselves at a defect as individuals, with the result that the magnetic method of testing for the detection of cracks, flaws, and the like, is rendered much more accurate and sensitive.

It is therefore an important object of this invention to provide a paste of paramagnetic particles containing a dispersingagent capable of upon dilution to form a bath for use in the detection of flaws by the magnetic method.

Other and further important objects of this invention will become apparent from the following description and appended claims.

In preparing a paste of paramagnetic particles for the .purpose described, various paramagnetic materials in finely divided powder form may be used, such as nickel, cobalt, paramagnetic aluminum alloys, iron, or various iron oxides, but I prefer to use the magnetic or black oxide of iron (moi). A dwuer ofa particle; size less.

than 10 microns and preferably less than '5 microns, is used.

In orderto accomplish the-initial dispersion for complete wetting of the individual particlesin this initial dispersion of the powder is. the,

same, or similar to that to be used in dilution I of the-pastetoformatesting bath.-' Sujmcient oil is employed in the".grindlng operation to're suit. in a stiff paste ofthe-p'owder and oil.

' In order to prevent agglomeration of the pare ticles and to. effect a uniform dispersion thereof bath, a dispersing agent is incorporated intoth e powder and oil, preferably during the grinding upon subsequent dilution informing the testing a I operation; A substance,"such as oleic or stearic acid, or a metal soap thereof, servcsyas a satis- 1 The amount of the V factory. dispersing agent.

dispersing agent required is in general-less than 5% and vneed be only sufiicient to be:eflective in the subsequent dilution of the paste to give a uniform dispersion of the paramagnetic particles and prevent rapid settling. thereof in the testing bath. If settling in the testing bath does occur, the dispersing agents facilitate theremixing of the settled out particles by preventing 4 the caking of the particles. As a result, the

paramagnetic particles in the flnaltesting bath show little if any tendency to agglomerate and are substantially free to act and .move as individuals in the bath. I

A preferred formula of the paste follows:

Per cent Black oxide of iron.- Light petroleum oil .37 Stearic acid- I '3 A light petroleum oil suitable for the'p'urpose is one having a Baum of 46 A. P; I., a Sa'yholt viscosity of 31 seconds, a flash point tag open cupof to R, an initial boiling point of 390 F. and an end boiling point of 490 ,F.', and a color of 25. Saybolt.

In preparing'a paste of the foregoing formula,

in which the percentages are by weight, the

and the mixture ground together in a mill. Any fine powder of a suitable paramagnetic material may besubstituted for the black oxide of iron.

Coal tar distillates. such as naphtha or benzol can be used in place oi the mineral oil distillate or as a blend therewith.

In making up the iinal testing bath, from 3 to 5 lbs. of the paste are added to 10 gallons of the same or a similar light oil to that used in the paste. The testing of a paramagnetic material for cracks, flaws, or the like is performed either .by immersing the article in the bath or by flowing some of the bath over the article ,in a magnetized condition and allowing the film adhering to the article to drain and dry. The article is then examined for cracks or flaws in the manner familiar to those acquainted with the magnetic method of testing.

I am aware that numerous details of the process may be varied through a wide range without departing from the principles of this invention, and I, therefore, do not purpose limiting the patent granted hereon otherwise than necessitated by the prior art.

I claim as my invention:

1. A plate for use in examining paramagnetic materials for flaws by the magnetic method, said amass:

paste comprising a uniform dispersion of finely divided paramagnetic particles in an oily vehicle and a small percentage of a dispersing agent eilective to prevent agglomeration oi! said particles and to disperse said particles upon dilution of said paste.

2. A paste for use in examining paramagnetic materials for flaws by the magnetic method, said paste comprising powdered black oxide of iron 01' less than 5 micron particle size, a light petroleum oil and a few percent 01' stearic acid effective to prevent agglomeration of said particles and to disperse said particles uniformly upon dilution of said paste.

3. A paste for use in examining paramagnetic materials for flaws by the magnetic method, said paste comprising 60% of powdered black oxide of iron 01 less than 5 micron particle size, 30% 01' a light petroleum oil and 3% of stearic acid effective to prevent agglomeration of said particles and to disperse said particles uniformly upon dilution of said paste.

- CARL E. BETZ. 

